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I’m pretty sure the MDF was 19mm which is pretty close to 3/4". I’ve resurfaced mine a few times though, using a wide flat bit to machine out the area covered by the cutter and a wood plane to remove the shoulder left around the edge where the cutter cannot reach.
I’m due to replace it all very soon because there"s only approx 1/8" left between the top of the centre rail and the top of the wasteboard - I’ve already marked the metal with a tool bit,although it did little more than remove the anodising.
@DavidWestley I’m about to remodel my spoil board after your own design but using sail track instead of t-track (cheaper).
As I understand it your spoil board is set up something like this (my version with sail track):
With 18mm MDF pieces between the 20x20 extrusion to which the t-track is fastened and then pieces of 18mm MDF between the t-track?
How are the first pieces of MDF fastened to the table top? How is the second layer of MDF fastened to the first?
I was going to use hollow wall anchors to fasten the first layer of 18mm MDF to the table top - only because my table top is the 9mm top skin of a torsion box so I can’t just screw into it. To fasten the second, sacrificial layer to the first, I was going to place some threaded inserts into the base piece and connect the sacrificial layer that way.
Would just using screws to hold the two MDF layers together work OK? My main concern is to get everything flat and solid with a reliable way to swap out the sacrifical boards I may be over thinking this hence the questions.
Unless my mathematics are at fault (entirely likely), The top of the spoil board should be 10mm above the t-track/sail tracks. Lots of room for mistakes and re-surfacing,
[quote=“GeoffSteer, post:46, topic:17870”]
With 18mm MDF pieces between the 20x20 extrusion
[/quote] How are you making up the 2mm difference or are you just ignoring it and any sag from screwing the layers together is negated when you flatten the top sacrificial surface?
I purchased some extra 20x20 alum extrusions to create more intermediate supports and just plan on resting the wasteboard across all of that. I do plan on integrating t-track but havent decided on that method yet though.
The middle track, sitting on top of the 20mm extrusion, will be 2mm higher than the other tracks but the sacrificial MDF pieces will all be at the same level as they sit directly on the base board.
@MichaelGrigg posted a link to this video which shows pretty much what I intend to do, except that my fixed waste board will sit between the extrusion, not on top of them.
Drilled the top skin of the torsion box today and sure enough, I messed up on one of the wall anchors. A miscalculation saw the hole drilled too close to the internal divider so the anchor wouldn’t hold. Not being too bright, it took me two anchors lost into the torsion box void to work this out.
What would have been a good idea would have been to make the top torsion box skin out of 18mm MDF…
Now you tell me! I think that block idea would have worked given there’s not a lot of load involved.
There are two pieces of MDF that go between the 20x20 extrusion and fasten to the torsion box, I think the only way to fasten those two together is via anchors.
I might use some of the now surplus threaded inserts from the old spoil board underneath these two bits of MDF so I have something to fasten the final sacrificial surface to.
@GeoffSteer Your table setup looks good & the rails should be fine.
I’m really no longer a fan of the threaded inserts into the MDF. Probably because I always over tighten things, but I’ve found that the threaded inserts have caused the surrounding MDF to “bulge” slightly upwards which affects the overall ‘flatness’ of the table. Perhaps this has been exacerbated by the hot humid weather we’ve been getting, but I doubt I’ll be putting the inserts back into my next lot of wasteboards.
The lower piece of wood is actually plywood. The upper layer of MDF sacrifical wood is simply screwed down with woodscrews which were tightened so that the head were 3-4mm below the surface (so I dont hit them when re-surfacing).
Finally got the spoilboard fixed down and ran a surface pass this morning. I had to adjust the Z axis a bit as it had quite a bad forward tilt.
I learned a couple of useful things:
The left hand side of my spoil board is (or was) about 2mm higher than the right so what started as 0.5mm light cut resulted in a (nearly) 2mm cut on the left and no cutting at all on the right.
My sacrificial boards don’t need to be 1000mm long. The rear 200mm or so doesn’t get cut so can’t be levelled so really don’t need to be there. (Handy to know if you intend to use t-track, you only need the 835mm long pieces.)
There’s a 15mm strip at the front that doesn’t get cut so i’ll plane that down.
The surface finish has some noticeable steps in the Y direction and these are more pronounced at the end of the Y axis travel. A bit of research needed to sort this one out. It makes a LOT of dust! Definitely need a dust show or at very least, an air flow diverter until I can get a dust shoe cut.
Ran a 22mm bit over the surface to level up the sacrificial boards but the surface ended up anything but level!
The passes vary in depth up to 0.25mm. I ran the same program in the X direction and same issue.
Belts, pulleys and v-wheels are tight, spindle is perpendicular in the X and Y planes. The g-code doesn’t move the Z axis after the initial plunge. I’m thinking flex or instability in the spindle mount (Makita RT0701 router). Anything else I could check?
It was sold as a bottom cleaning bit, the biggest I could find with a 1/4" shaft.
The profile of each pass is OK - flat bottomed without one edge higher/lower than the other, but each pass is at a slightly different different Z height. Its seems more pronounced at the front and rear of the X-Carve when cutting in the Y direction. Not sure about when cut in the X direction as I stopped the job whan I saw the same symptoms in the first few passes.
I do but haven’t done any measurements on this, the 0.25mm variance is what you might call an educated guess.
EDIT Looking a bit closer it seems that each alternate pass is in error. On the off chance that it’s direction related, I’m going to run a new surface program that only cuts in one direction.
As this rate, I’ll be replacing the sacrificial boards sooner than I expected.
EDIT:EDIT Well that didn’t work. I ran a program to surface in the X direction, from left to right than a rapid move back to the left for the next pass. Whereas in the Y direction job, each pass seemed to be at a different level (up/down) from the previous one, this run had the front part of the cut higher than the rear indicating a tilted spindle (yes?).
The right hand side of the spoil board was nearly perfect, no obvious difference between cuts but on the left hand side, the difference in the passes is very much evident.
More testing tomorrow, I’ve breathed my limit of MDF dust for the day.
